THE RADIOACTIVITY OF SOME RUTHENIUM AND ERBIUM ISOTOPES DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By BASANT LAL SHARMA, B. Sc., M. Sc. The Ohio State University 1959 Approved by: " - y n - L . t o J Z ------------------ x a s i s e r ----------^ -------- Department of Physics and Astronomy Acknowledgm ent I take this opportunity to express my sincere appreciation to Professor M. L. Pool for his interest, suggestions, and encouragement throughout this work. Table of Contents Page General Introduction ................................................................................................. 1 Instrumentation ................................................................................................................................ PART I RADIOACTIVE DECAY OF Ru106 AND THE ESTIMATION OF THE THERMAL NEUTRON ACTIVATION CROSS SECTION OF Ru105 Introduction........................................................................................................................................... 8 Experimental D ata............................................................................................. 11 Calculation of the Thermal Neutron Activation Cross Section of R u ^ ^.....................................................................................................23 Results and Discussion............................................................................................... 28 Bibliography ............................................ ........................................................................ 30 PART II RADIOACTIVE DECAY OF Rh101 Introduction...........................................................................................................................................31 Experimental D a ta ................................................................................................................... 33 R esults .....................................................................................................................................................49 Discussion and Conclusions .............................................................................................51 Bibliography ............................................................................................................................. 55 Table of Contents (continued) Page PART in RADIOACTIVE DECAY OF Er171 AND A SEARCH FOR RADIOACTIVE DECAY OF Er172 Introduction.......................................................... 56 Experimental D a ta ......................................................................................... 58 Results and Conclusion................................................................................................ 75 Bibliography .................................................... 78 Autobiography........................................................................................................................... 79 iv List of Tables Page Table I Isotopic Composition of Natural Ruthenium and the Purity of the Sample labeled Ru - 104 ................................................. 11 Table II Isotopic Composition of Natural Ruthenium and the Composition of the Enriched ............................................................................................... 3 3 Table III Isotopic Composition of Natural Erbium as Compared with that of Enriched Er170 ..................................................................................... 58 Table IV Spectrographic Analysis of Enriched Er170 ..................................................................................... 5 9 v List of Figures “ge Nal (Tl) Well Type Crystal Arrangement 4 100-Channel Pulse Height Analyzer . 6 _ 106 106 Decay Scheme of Ru - Rh ..................... 10 103 Decay of the Gamma Ray due to Ru . 1 3 Gamma Ray Spectrum of Sample N-809, 19 Days after Irradiation . 14 Comparison of the Gamma Ray Spectrum of the Sample N-809 with that of: 27127 0 Day-Ag^® • • 15 106 Gamma Ray Spectrum of Rh 19 1 O A Gamma-Gamma Coincidence Spectrum of Rh 21 Gamma-Gamma Coincidence Spectrum of Sample N-100 9 (Ru106 - Rh1 °6) .................................... 22 Gamma Ray Spectrum of Sample N-1119 .... 35 Gamma Ray Spectrum of Ru^^ + p (N-1119) . 37 545 kev Gamma Decay of Rh^ ^ ......... 38 Gamma Ray Spectra of Rh^^ (Sample N-1124) . 39 310 kev Gamma Decay of Rh^-^ ......................................... 41 Copper and Lead Absroption Measurements . 42 Gamma-Gamma Coincidence Spectrum of Rh"*"^ 44 Comparison of the Gamma Ray Spectrum of Ru ^ + p (N-l 119) with that of Ru + d (N-791) 46 vi List of Figures (continued) F igure Page 18. Gamma-Gamma Coincidence Spectrum of Sample N-791 (Ru + d ) ................................................................. 48 19. Proposed Decay Scheme of ................................. 54 170 20. Gamma Ray Spectra of Er + n (N-1031) . 6 0 2 1 . 308 kev Gamma Decay of (N-1031) .... 62 22. Gamma Ray Spectrum of Sample N-1031...................... 63 23. Gamma-Gamma Coincidence Spectrum of Er171 (Sample N-1031).................................................................. 65 24. Gamma Ray Spectrum of Yb Fraction............................ 67 25. Well Crystal Measurements of E r^^ (N-1090) . 69 26. Gamma Ray Spectra of Sc^^, La^^, and Yb^7~* Impurities in Sample N-1096 71 27. Gamma Ray Spectra of Tm^ 7^ (Test Tube No. 20) t Tm169 + n (N-1091), and Er170 + n (N-1096) ................................................................................. 73 28. Copper Absorption Gamma Ray Spectra of Er170 4 n ...................................................................................................... 74 1 71 29. Decay of Scheme of Tm ............................................................ 76 General Introduction Gamma ray scintillation spectrometry has developed greatly in recent years. The reasons for its development are manifold, but the most important one is that the detailed analysis of nuclear radia­ tion yields information about the properties of nuclear levels, which are of basic importance for our understanding of nuclear matter and for the development of nuclear theories, such as the theory of nuclear shell structure. Scintillation counting offers three primary advantages for the detection of gamma rays. First, resolving times of the order of millimicroseconds allow high speed counting with no resolving time corrections. Second, the output pulse height generated by the scintillation detector is proportional to the amount of energy dissi­ pated in the scintillator by the incident gamma ray. Third, the fact that the sensitive volume is usually a solid results in approximately a hundredfold increase in efficiency over gas counters. The availability of enriched isotopes, various types of bom­ barding particles, higher neutron flux, and other improved modern techniques have made it possible to study nuclear reactions in greater detail and thus obtaining new information together with confirming previous data. It is true that the modern techniques are capable of analyzing complex spectra, but at the same time in some cases the spectra have become more complicated because of them. For example, on one hand, the availability of higher thermal neutron flux has made it possible to study the decay of radioactive isotopes formed by double thermal neutron capture or decay of radioactive isotopes having very low capture cross sections; on the other hand, it has been able to superimpose the spectra of impurities which are present in very small quantities but have relatively higher thermal neutron cross sections. However, the importance of the above mentioned techniques cannot be challenged. The study of the neutron capture cross sections of stable and radioactive isotopes is also of great importance because an extensive knowledge of them may show further interesting regularities and may assist in accounting for the abundances of elements. Keeping these basic points in mind, the following investiga­ tions were undertaken. The dissertation is divided into three parts. The first part concerns the study of radioactive decay of Ru^^ from which it was possible to calculate the thermal neutron activation cross section of Ru^^, The second part deals with the detailed study of the decay of Rh^^. In the third part of this dissertation radio- 171 active decay of Er together with a search for radioactive decay of £.r172 hag been studied. In all the above investigations, the en­ riched isotopes obtained from Oak Ridge were used. Instrumentation The choice of detector and the source-detector configuration largely depend on the activity of the isotope under examination, and will be discussed later for each of the isotopes separately. The following is a brief description of the various types of instruments and techniques which were used. Scintillation Detectors The detector, known as flat crystal in this laboratory, was composed of a 1- 3/4- x 2" cylindrical Nal (Tl ) crystal, a DuMont 6292 photomultiplier tube, and a white cathode follower designed at Oak Ridge National Laboratory. The pulses from this detector were fed into a 100-channel analyzer. Another type of scintillation detector used was the well type crystal, which is shown in Fig. 1. This detector consisted of a 3" x 3" cylindrical Nal (Tl ) crystal with a 3/8" hole which extended along the longitudinal axis to the center of the crystal, a DuMont 6 3 94 (5 inches) photomultiplier tube and a